Photographing the gas giants

18 July 2016

Interview with

Roger Hutchinson, Astrophographer

Roger Hutchinson takes Graihagh Jackson through how he photographs the night sky
Roger Hutchinson in his observatory...

Roger - Well, when I was a kid -  I grew up in the 70's and that was right at the tail end of the Apollo programme. So the moon landings and everything, as a young boy, really inspired me and an interest in space developed. And then as I got a little bit older, probably with the encouragement of my dad, I built a telescope and I can still remember the first time I saw Saturn through telescope and that kind of hooked me. I did a lot of astronomy as a kid growing up and then went away to University, kind of dropped out for a bit - just got on with life, and then probably about 5 or 6 years ago I got back into the hobby. I've been obsessively photographing the skies ever since really.

Graihagh - You mentioned Saturn. You said you'll always remember the first time you saw Saturn. I wonder whether you could describe that moment a bit more for me?

Roger - Well, when you see it with your own eyes for the first time, it kind of blows you away. People think it's something that's been stuck onto the end of the telescope; they just think it's a little cardboard cutout or something because it just doesn't look real you know - it's mind-blowing really!

Graihagh - OK. I will add that to my checklist of things to do in life: catch a fish and eat it, see Saturn in the real flesh. I think that's the next one to do.

So tell me about Jupiter then? Have you photographed Jupiter much and I want to know is it disappointing to see?

Roger - No, I would say Jupiter is not disappointing! I have done a lot of photography of Jupiter. For planetary photography it's probably the easiest target because it's not called the king of the planets for nothing. It's big and it's an interesting sort of target as well because it rotates so quickly, the cloud patterns change. It's quite a dynamic target so it's a good one to cut your teeth on.

Graihagh - I came all the way to your beautiful house in the hope that we might be able to photograph Jupiter, and classically it's cloud in the U.K. What more would you expect?

Roger - In astronomy in Britain you've just got to develop a lot of patience and just realise that there'll be another opportunity some other time and just make the most of what nature deals you,  but this summer has been particularly bad.

Graihagh - You say it's a write off, but I'm looking into your back garden as we sit in the conservatory now and I think the whole trip down from Cambridge has been worth it just to see... I mean I don't even know how to describe it, it's like a mini observatory in some ways - it's quite impressive!

Roger - Well I guess it's what people would picture if they were talking about an observatory; it's got a dome. So like anything with a...

Graighah - Seriously - I think you're underselling it here! It's a good two metres high, white and almost like a hidey house at the back of the garden.

Roger - It's been described as a minion, a rubbish bin, a portable toilet... all sorts of things. There's been a lot of comments about it

Graighah - Can you give me a tour?

Roger - Absolutely... So it's all plugged in in the hope that we'd see something but... Just watch yourself here as I have bashed my head on numerous times.

Graihagh - It's a really impressive setup.

Roger - It's currently pointing at Jupiter at the minute but you wouldn't know it

Graihagh - Does that mean you're sitting out here for hours on end or do you just hit click and then go to bed?

Roger - Well for planetary, you're actually shooting video, so you don't take individual images; you take a sequence of individual images. Basically what we call it is 'lucky imaging' because the sky and the atmosphere is very turbulent and the more you magnify it the more turbulent it becomes so, basically, it's what we call 'seeing'.  Seeing is basically with front distortions in the atmosphere, so it's just like if you're looking at something under high magnification - it wobbles. What you want to do to counteract that is shoot something when it's really high in the sky so you're looking through less atmosphere, or you can use different wavelengths of light that are less affected by seeing. Or you could wait to get a really good night because that is the best thing to let nature sort it out for you.

So there are lots of websites that have jetstream predictions. So what you want is the wind speed of the jetstream to be low over the U.K., over where you're imaging. And then in general, it doesn't always hold true but, in general, if you've got light winds at ground level, light winds in the jetstream, then seeing is normally reasonably good.

So the best thing is to take in when everything works well for you. But we can help that along by using a non-visible wavelengths pass filter and what that does is if you think about the electromagnetic spectrum and you've got like red through to...

Graihagh - Like the rainbow...

Roger - Like the rainbow, basically. So red is a longer wavelength than green, which is a longer wavelength than blue. So what I do is image through a mono camera, so this is a black and white camera, and you image through a series of different filters. What we use is an infrared pass filter which filters out any wavelength shorter than 685 nanometers, so it's quite long wavelengths, and that is less affected by seeing - the shorter wavelengths are more affected by seeing.

So what you typically see when you're taking your images, you take a series of images; one through an infrared filter, which is not necessary if you want a colour image, you can just use a red and then a green, and a blue filter. But what you generally see is that the red filter image is less affected than the blue filter image by atmospheric seeing because red light has a longer wavelength than blue light so it kind of demonstrates the theory quite well.

Graihagh - You must have to brush up on your physics quite a lot here t work out how well to photograph these things?

Roger - You don't necessarily need to know the physics; you're just shooting through different filters but it's quite nice to know why your red image is much better than your blue image. But what we then tend to do is we'll combine the red, green, and blue images together to give you a colouridge and then we'll use the infrared image as what's termed a luminance layer, which is where all your detail is.  So that sits on top and gives you all the detail, and all the colour comes from the red, green and blue images that you've taken through the relevant filters.

Oh, that was the dome moving...

Graihagh - It moves automatically?

Roger - Yes, it's tracking the sky as well as the telescope. So what that does mean to answer your earlier question, you can, if you're taking long exposure photographs of deep sky objects, you can set it going and go off and have a cup of tea in the warm.

Graihagh - And the roof will continue to move round?

Roger - And the roof will move around for you, yes. It does give you a little bit of shock sometimes if you're not expecting it or if you're leaning against it!

Graihagh - Rooky error!

Roger - I'd forgotten it was on actually. I'll turn it off because we're not actually looking at anything at the minute.

Graihagh - Back inside, Roger took me through the complicated imaging process he does to make these beautiful pictures. He really does make it look easy but actually, there's at least a good 45 minutes of tinkering around.

Roger - You take a lot of images over time and some are better than others and a lot of it, as I've said, is down to conditions that are basically beyond your control. Sometimes you just get a perfect night where everything just works well, works in your favour, all the equipment works well, and you get a really nice image at the end of it. It's about being patient, and plugging away, and not being too disheartened. It just that nice surprise when you get a really good result.

Graihagh - What image are you most proud of?

Roger - The one's I'm proudest of are probably some of the deep sky images because they do take a lot of time and dedication. But the ones I like the most and enjoyed taking the most are probably the transitory ones. The lunar eclipse that we had last September - it was just great for the weather to play ball because these things happen quite rarely, and so to be able to actually get them and image them is exciting and really pleasurable.

Graihagh - I can see... I can see you take great joy - watching your process and talking about it - I can see it gives you great pleasure.

Roger - Mmm. Absolutely! I can recommend it to anyone. You don't need to go mad and have your own observatory in the back yard to do it either. You can create really nice results with minimal gear.

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